Sideplate for turbine blade

ABSTRACT

Sideplate structure for sealing a chamber between adjacent turbine blades in the periphery of a rotor disc is disclosed. The periphery of the disc is provided with side entry channels for receiving the root portions of rotor blades having radial cooling holes extending from the root portions through the tips of the blades. The channels provide an axially extending passageway communicating with the cooling holes whereby a cooling fluid flows through the passageway and into the holes to cool the blades. Sealing plates are provided for closing the downstream end of the passageways. A sideplate is provided for each pair of adjacent blades and is disposed on one side of the pair of blades to seal the downstream end of the space between the adjacent blades. The sideplate has a generally T-shaped configuration with an upper main body portion and lower arms extending from the main body. Means are provided on the blade extensions of the rotor blades defining a groove, one side of which on one rotor blade being complementary in shape to the other side thereof on another rotor blade positioned adjacent said one rotor blade. With two blades positioned adjacent each other a generally U-shaped groove having generally circumferentially extending lower sections is defined between the blades. The U-shaped groove is shaped and sized to snugly and slidably receive the sideplate. Locking means are provided for securing the sideplate against unlimited radial downward movement with respect to adjacent rotor blades.

Hugoson et al.

[ 1 July 24, 1973 SIDEPLATE FOR TURBINE BLADE [75] Inventors: Birger O.Hugoson, Wallingford, Pa.;

, Norbert Vettel, Offenbach/Main,

Buergel, Germany [73] Assignee: Westinghouse Electric Corporation,Pittsburgh, Pa.

2 2 Filed: Sept. 14, 1971 2'11 App1.No.: 180,375

[52] US. Cl 416/92, 416/96, 416/220 7 Primary Examiner-Carlton R. CroyleAssistant Examiner--Robert E. Garrett Attorney-A. T. Stratton et al.

571 a 2 ABSTRACT S ideplate structure for sealing a chamber betweenadjacent turbine blades in the periphery of a rotor disc is disclosed.The periphery of the disc is provided with side entry channels forreceiving the root portions of rotor blades having radial coolingholesextending from the root portions through the tips of the blades.

The channels provide an axially extending passageway communicating withthe cooling holes whereby a cooling fluid flows through the passagewayand into the holes to cool the blades. Sealing plates are provided forclosing the downstream end of the passageways.

A sideplate is provided for each pair of adjacent blades and is disposedon one side of the pair of blades to seal the downstream end of thespace between the adjacent blades. The sideplate has a generally,T-shaped configuration with an upper main body portion and lower armsextending from the main body. Means are provided on the blade extensionsof the rotor blades defining -a groove, one side of which on one rotorblade being complementary in shape to the other side thereof on anotherrotor blade positioned adjacent said one rotor blade. With two bladespositioned adjacent each other a generally U-shaped groove'havinggenerally circumferentially extending lower sections is defined betweentheblades. The U-Ishaped groove is-shaped and sized to snugly andslidably receive the sideplate. Locking means are provided for securingthe sideplate against unlimited radial downward movement with respect toadjacent rotor blades.

12 Claims, 7 Drawing Figures Patented July 24, 1913 3,748,060

3 Shea til-Sheet 1 Patghted July 24, 1973 3 Sheets-Sheet 2 SIDEPLATE FORTURBINE BLADE BACKGROUND OF THE INVENTION The present invention relatesgenerally to turbine rotors and particularly to a structure for sealingthe downstream end of the chamber between adjacent turbine bladesmounted on the rotor disc.

It is a well known practice to use sideplates to secure turbine rotorblades of the side entry type in a rotor disc of an axial flow turbine.In some turbine blade and rotor disc arrangements, sideplates are fittedinto grooves formed on both the upstream and downstream sides of theblades and disc, respectively, with the sideplates also serving to sealthe root portions of the blades from the motive fluid and to regulatethe flow of cooling fluid passing the root portion of the blades. Inother arrangements, as where the entire turbine blades are cooled bycooling fluid flowing through radial holes in the blades, the blades areabutted against a ledge of an upstream sideplate mounted on the rotordisc and sideplates are arranged in grooves formed on the downstreamside of the blades for securing the blades to the disc.

I In many of the known sideplate arrangements, sealing is effected byoverlapping the side edges of adjacent sideplates." This overlappingdesign requires that the sideplates be installed sequentially around therotor disc and then locked in place with specially shaped lockingplates. In order to remove one turbine blade or one sideplate, all ofthe sideplates to one side thereof must be removed. This is a timeconsuming and expensive procedure.

The known sideplate structures are alsosubject to buckling when they areplaced under stress due to the centrifugal force attendant with rotationof the rotor disc. Since the sideplates-are fixed at their upper edgesin the groove that is provided,-the centrifugal force will urge theupper edge of the sideplate against the surface of the. groove tothereby place the sideplate under compressive stress. Should thesideplate not be strong enough, it will eventually buckle and have to beremachined, the overlapping will be improper with an ineffectivesealresulting. Anybuckling of the sideplates will also result inseparation of the overlapping and reduction of the sealingeffectiveness.

It is desirable in turbines to have the airfoil portion of the turbineblades as far as possible away from the periphery of the rotor disc. Thefarther away the airfoil is, the cooler will be the rotor disc with thedisc thus having a longer useful life. In addition, less expensivematerial could be used to construct a rotor disc operated at lowertemperatures. The blade extensions between the blade platform and theroot portion are lengthened for increasing the separation of the airfoilfrom the rotor disc. With the presently known sideplates, increasing theblade extensions is limited since any increase of the length of theblade extensions would require'an increase in length of the sideplates.

Increasing the length of the sideplates increases their susceptibilityto buckling and diminishes their sealing effectiveness since a greaterradial length along the side BRIEF SUMMARY The present inventionovercomes the undesirable features noted above with respect to the knownsideplate structures. Thus, the present invention provides a simplesideplate structure which is easy to assemble and disassemble and may besingly removed and re- 1 placed, is shaped to provide an effective seal,and is shaped and arranged for diminishing the tendency to buckle,thereby permitting a thinner construction. The noted advantages resultfrom the novel sideplate structure of the present invention which is.generally T- shaped and is used in association with a pair of adjacentturbine blades mountedin axially extending channels provided in theperiphery of a rotor disc. The turbine blades are provided with radialholes for receiving cooling fluid flowing in a passageway provided inthe channels of the rotor disc. A sealing plate is provided for closingthe downstream end of the passageway; Means are provided on the bladeextension of each turbine blade for defining a groove, one side of whichon one rotor blade is complementary in shape to the other side of thegroove on another blade. Thus, when two rotor blades are positonedadjacent each other, a continuous groove is formed between them, thegroove being generally U-shaped and having generally circumferentiallyextending lower sections, the U-shaped groovebeing shaped to snugly andslidably receive the T-shaped sideplate. The sideplate is securedagainst unlimited radial downward movement by suitable locking means,such as a removable rivet through the sideplate arranged to engagethetop of the rotor disc steeple located between the adjacent turbineblades. When the rotor disc is rotatedat high-speeds,.the sideplate willmove radially outwardly in the U-shaped groove due to the effect ofcentrifugal :force. The stress 'on the sideplate will be borne by itsarms thereby placingthe.

upper section of the sideplatein tension which is prefer'able over thecompression to which the known sideplates are subjected. In thepreferred embodiment, the lower extensions of the U-shaped grooves areprovided with a bevel in the radially divergent direction and the upperedges of the armsof the sideplate are provided with complementary shapedbevels on the upper edges. Thus, when the sideplates move upwardly underthe urgingof centrifugal force, a wedging action results'to provide apositive and effective seal.

THE DRAWINGS FIG. 2 is a partial side elevation view of a rotor discshowing turbine blades secured therein by sideplates in accordance withthe principles of the present invention;

FIG. 3 is a view taken along the line III-III of FIG. 2;

FIG. 4 is a view taken along the line IVIV of FIG.

FIG. 5 is a view taken along the line V--V of FIG. 2;

FIG. 6 is a perspective view of turbine rotor blades and a portion of arotor disc showing sideplate structures securing blades to the rotordisc in accordance with the invention; and

FIG. 7 is an elevation view of a sideplate forming part of the presentinvention.

PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 shows aradial portion of a rotor 10 of an axial flow turbine in longitudinalsection. The rotor 10 may comprise an aggregate of rotor discs, only oneof which 12 is shown, secured together by circumferentially disposed tieor stay bolts extending through the discs.

The rotor'disc 12 is a first stage disc and supports turbine blades 14extending radially outwardly therefrom, the blades being disposedbetween axially spaced inwardly extending fixed vanes or nozzle blades16 and 18. The turbine blades 14 are provided with an airfoil shapedvane portion 19 and a root portion 20 of the side entry type which maybe of the serrated or flr tree type for disposition in axially extendingserrated channels 22 formed in the outer periphery of rotor disc 12, asshown in FIG. 2. The lower or radial inward portion of the channels 22are formed and sized to provide a clearance with the lower end of rootportion 20 which clearance serves as a passageway 24 for directingcooling fluid between the root portion and the rotor disc as shown. Thepassageway 24 communicates with radial cooling holes or bores 26extending from the bottom of the root portion 20 of the blades 14through the tips of the airfoil portion19 thereof. The turbine blades 14are further provided with.the usual platform 28 and a blade extension 30between the platform and the root portion The rotor disc 12 is alsoprovided with a passageway 32 at the upstream side thereof, and formedby an upstream sideplate 34 secured to the upstream face of the mainbody portion of the rotor disc by circumferentially disposed tiev bolts36 extending through the upstream sideplate and rotor disc, only one tiebolt being sho wn'in FIG. 1. Passageway 32 is arranged to communicatewith passageway 24 in the manner shown. An air separator plate 38 issecured to upstream sideplate 34 in any well known manner, with theseparator plate and upstream sideplates shaped to define a passageway 40communicating with passageway 32. Passageway 40 is connected with asource of cooling fluid, not shown, whereby the cooling fluid will flowthrough the intercommunicating passageways 40, 32, and 24 and throughradial cooling bores 26 for cooling the turbine blades 14.

The upstream sideplate 34 is formed with a radial outer, annular ledge44 arranged to extend from the top radially outer surface of passageway24 to slightly beyond a curvilinear plane defined by the radiallyoutermost portions of a plurality of steeples 46 disposed on the rotordisc 12. The ledge 44 serves as the upstream Each pair of the adjacentturbine blades 14 mounted in the channels 22 of rotor disc 12 has asideplate 50 mounted on its downstream side, adapted to seal a void 51formed by the adjacent blades 14. Each turbine blade 14 has a generallyT-shaped blade neck 52 on the downstream side thereof, and extendingfrom the blade platform 28 to an intermediate point on the bladeextension 30. The blade neck 52 has a radially extending, centrallydisposed center section 54 and generally circumferentially extendingupper side sections 56 and 58. The outer edges of the center section 54and upper side sections 56 and 58 are spaced from the opposing surfaceof the blade extension 30 to.define a continuous groove having uppergroove sections 60a and 60b along'the side sections 56 and 58 and theradial expance of each side of center section 54, and lower groovesections 62a and 62b at the circumferentially extending portions of thecenter section 54. The upper groove section 60a and lower groove section62a of one turbine blade 14 would, thus, be complementary in shape tothe upper groove section 60b and lower groove section 62b of anotherturbine blade 14 arranged in rotor disc 12 adjacent the first blade.With a pair of turbine blades l4arranged adjacent each other, agenerally continuous U-shaped groove is defined between the upper andlower groove sections of one side of one blade and the upper and lowergroove sections of the other side of the other blade. The U-shapedgroove between thetwo adjacent turbine blades 14 has a central section(60a and 60b) and opposite generally circumferentially extending lowersections (62a and 62b). As shown in the drawings, the uppermost portionsof upper groove sections 60a and 60b are circular in outline wherebywhen the U-shaped groove is formed between adjacent turbine blades asemicircular groove is defined at the upper region thereof.

As shown in FIG. 4, the cross-sectional shape of the upper groovesections 60a and 60b are generally rectangular. The lower groovesections 62a and 62b are, as shown in FIG. 3, provided with abevelledinner surface, the inclination of the level in a radially divergentdirection with respect to rotor disc 12.

Each sideplate 50 is shapedto besnugly and slidably received in theU-shaped groove defined between adjacent pairs of turbine blades 12.Each sideplate 50 has a main body portion having a generallysemicircular shaped upper section 72, and arms 74 and 76 extendinggenerally circumferentially from a lower portion of the main body 70.The outer edges of main body 70 are sized and shaped to snugly fitwithin the upper groove sections 60a and 60b in the manner showngenerally in FIG. 2. The upper edges of arms 74 and 76 are provided witha bevel complementary in shape to the bevelled surface of lower groovesections 620 and 62b. The edges of arms 74 and 76 will engage thesurface of lower groove sections 62a .and 62b in the manner shown inFIG. 3. Each sideplate 50 is simply installed by sliding it along thesurface of the steeple 46 between an adjacent pair of turbine blades 14and into the U- shaped groove defined between the blades.

Each sideplate 50 is secured against unlimited radial downward movementwith respect to the rotor disc 12 by means of a lock rivet 80 insertedin an opening through an intermediate portion of the sideplate 50. Thelock rivet 80 is arranged to engage the top of a steeple 46 of rotordisc 12. The lock rivet 80 is of any well known configuration and issimply installed by inserting the blank rivet in the opening throughsideplate 80 and expanded by striking the rivet with a locking tool. Forremoval, the lock rivet 80 is hit with a convex toolthat stretches therivet into a generally cylindrical shape to permit the rivet to besimply removed from the opening of the sideplate 50. It should be noted,however, that any other suitable removable locking device, such as alocknut, could be used 'to secure a sideplate 50 against moving radiallyinwardly of the rotor disc 12. v As the rotor disc 12 is rotated, acentrifugal force will be imparted to the sideplates 50 which will, atthe higher disc speeds, cause the sideplates 50 to move radiallyoutwardly in the U-shaped grooves. Each sideplate 50 is sized such thatthe arms 74 and 76 will engage the lower groove sections 62a and 62bwith a clearance existing between the upper section 72 of the sideplateand the opposite'upper surfaces of the upper groove sections 60a and60b. Thus, the'stress on the sideplates 50 resulting from the effect ofthe centrifugal force imparted thereto will be borne by the arms 74 and76 thereby,,pl acing the main body 70 of the sideplate under tension.Such a condition of tension on the main portion of the sideplates 50,rather than compression as wouldbe the case if the, upper section of thesideplates bore the stress from the centrifugal force, reduces thepossibility of buckling of the sideplates 50.

. The clearance between the upper section 72 of the sideplates 50 andthe-opposite groove surface insures that the stress on the sideplates 50is home by the arms 74and76. f v

As the sideplates 50 movewradially outwardly under .the urging ofcentrifugal force, the bevel edges of arms 74 and 76 engagethe bevelledsurfaces of lower, groove sectionsv62a and 62b to therebyforce thesideplate up against the surface of the blade extension 28 andsteeples-46. Thus, a tight fit is realized between the side- 50 permitslonger blade extensions 28 which would resalt in a cooler rotor disc 12thereby lengthening the useful life of the disc and allowing the use ofless expensive material of use in constructing the disc. in addition,each of the sideplates 50 may be assembled and disassembledindividually-without moving the adjacent sideplates.

Though the invention has been shown and described in preferred form, itwill be obvious to those skilled in the art that it is not so limited,but is susceptible of many changes without departing from the spirit andscope thereof. 1

' We claim:

1. In a rotor for an axial flow fluid machine, the rotor comprising atleast one rotor disc with a plurality of spaced channelsprovided in theperiphery thereof for receiving the root portions of a plurality ofrotor blades having'radial cooling bores extending from the rootportions through the tips of the blades, a passageway extending axiallyand disposed radially inwards of each of the root portions, saidpassageways communicating with the cooling bores and being capable ofconducting a flow of cooling fluid therethrough, a steeple betweenadjacent channels on the periphery of the disc, a chamber disposedradially outwards of the steeples between adjacent blades, and sealingmeans closing the downstream end of the passageways, the improvementcomprising: V v

a side plate associated with each pair of adjacent blades and disposedon one side of said pair ,of blades for sealing one end of said chamberbetween I adjacent blades;

said sideplate having a generally T-shaped configuration with a bodyportion and arms extending from the body portion; platform extension onsaid rotor blades having meansdisposed thereon for definingagroo've,'one side of which on one rotor blade is complementary in shapeto the other side thereof on another rotor blade positioned adjacentsaid one rotor blade, whereby when said rotor blades are positionedadjacent, the groove defined, has a generally i U- shaped section and agenerally circumferentially extending radially inward section, saidU-shaped section being shaped to slidably receive said sideplate, andlocking means for securing said sideplate against unlimited radialinward movement with respect to said rotor disc. V .7 I 2. The structurerecited in claim 1 in which said arms of said sideplate are sized andshaped to engage said groove defining means during rotation-of saidrotor disc in such a. manner that the centrifugal force acting on thesideplate is borne by said arms with said body of said sideplateradially outward of said arms being in tension. h

3. The structure as recited in claim 1 in which said radially inwardcircumferentially extending sections of said grooveare bevelledin aradially divergentdirection, and said 'armsof said sideplate areprovided with bevelled radially outward edges complementary in shape tothe bevelling of saidradially inward circumferentially extendingsections of saidgroove.

4. The structure recited in claim 2 in which said body portion of saidsideplate is sized such that during rotation of said rotor disc aclearance will exist betweenthe radially outward edge of said bodyportion and the 'opposite face of said U -shaped section of saidgroove.-

5. The structure recited in claim 1 in which saidlocking means comprisesa removable member extendingthrough an intermediate portion of said bodyportion of said sideplate in-a position to engage the radially outwardportion of the rotor disc steeple located between said pair of adjacentblades.

6. The structure recited in claim 5 in which said removable member is alock rivet.

7. In a rotor for an axial flow fluid machine, the rotor comprising atleast one rotor disc with a plurality of side entry channels provided inthe periphery thereof for receiving the root portions of a plurality ofside entry rotor blades having radial cooling bores extending from theroot portions through the vane portions of the blades, a passagewayextending axially and disposed radially inwards of each of the rootportions, said passageways communicating with the cooling bores andbeing capable of conducting a flow of cooling fluid therethrough,steeples between adjacent channels on the periphery of the disc, achamber disposed radially outwards of the steeples and between adjacentblades, and sealing means closing the downstream end of the passageways,the improvement comprising:

a sideplate associated with each pair of adjacent blades and disposed onone side of said pair of blades for sealing one end of said chambersbetween adjacent blades;

each rotor blade being provided with an extended blade neck portion, ablade platform portion, said platform having a ledge on its downstreamside defining a generally radially inwardly directed groove, a portionof each groove being more radiallyinward and said radially inwardsections defining a generally circumferentially extending section of thegroove; said groove sections at one side of any of said rotor blades,being complementary to the groove sections at the other side of anotherrotor blade whereby when two rotor blades are positioned adjacent eachother a continuous generally U-shaped groove is defined for securingeach side plate on the downstream side of two respective adjacentblades;

said sideplate having a body portion having edges to slidably fit withinthe radially outer groove sections of said U-shaped groove configurationbetween adjacent rotor blades, and arms extending generallycircumferentially from a radially inward portion of said body and havingradially outer edges of said arms shaped to snugly fit within theradially inward groove section of said U-shaped groove; and

locking means for securing said sideplate against unlimited radialinward movement with respect to said disc.

8. The structure recited in claim 7 in which said arms of said sideplateare sized and shaped to engage said side sections of said blade neckduring rotation of said rotor disc in such a manner that the centrifugalforce acting on the sideplate is' borne by said arms with said body ofsaid sideplate radially outward of said arms being in tension.

9. The structure recited in claim 7 in which said radially inward groovesections are bevelled in a radially divergent direction, and said armsof said sideplate are provided with bevelled radially outward edgescomplementary in shape to the bevelling of said radially in wardgenerally circumferentiallyextending groove sections.

10. The structure recited in claim 7 in which said locking means is aremovable member extending and the opposite face of said U-shapedsection of said groove.

12. The structure recited in claim 10 in which said removable member isa lock rivet.

* i t t

1. In a rotor for an axial flow fluid machine, the rotor comprising atleast one rotor disc with a plurality of spaced channels provided in theperiphery thereof for receiving the root portions of a plurality ofrotor blades having radial cooling bores extending from the rootportions through the tips of the blades, a passageway extending axiallyand disposed radially inwards of each of the root portions, saidpassageways communicating with the cooling bores and being capable ofconducting a flow of cooling fluid therethrough, a steeple betweenadjacent channels on the periphery of the disc, a chamBer disposedradially outwards of the steeples between adjacent blades, and sealingmeans closing the downstream end of the passageways, the improvementcomprising: a side plate associated with each pair of adjacent bladesand disposed on one side of said pair of blades for sealing one end ofsaid chamber between adjacent blades; said sideplate having a generallyT-shaped configuration with a body portion and arms extending from thebody portion; a platform extension on said rotor blades having meansdisposed thereon for defining a groove, one side of which on one rotorblade is complementary in shape to the other side thereof on anotherrotor blade positioned adjacent said one rotor blade, whereby when saidrotor blades are positioned adjacent, the groove defined, has agenerally U-shaped section and a generally circumferentially extendingradially inward section, said U-shaped section being shaped to slidablyreceive said sideplate, and locking means for securing said sideplateagainst unlimited radial inward movement with respect to said rotordisc.
 2. The structure recited in claim 1 in which said arms of saidsideplate are sized and shaped to engage said groove defining meansduring rotation of said rotor disc in such a manner that the centrifugalforce acting on the sideplate is borne by said arms with said body ofsaid sideplate radially outward of said arms being in tension.
 3. Thestructure as recited in claim 1 in which said radially inwardcircumferentially extending sections of said groove are bevelled in aradially divergent direction, and said arms of said sideplate areprovided with bevelled radially outward edges complementary in shape tothe bevelling of said radially inward circumferentially extendingsections of said groove.
 4. The structure recited in claim 2 in whichsaid body portion of said sideplate is sized such that during rotationof said rotor disc a clearance will exist between the radially outwardedge of said body portion and the opposite face of said U-shaped sectionof said groove.
 5. The structure recited in claim 1 in which saidlocking means comprises a removable member extending through anintermediate portion of said body portion of said sideplate in aposition to engage the radially outward portion of the rotor discsteeple located between said pair of adjacent blades.
 6. The structurerecited in claim 5 in which said removable member is a lock rivet.
 7. Ina rotor for an axial flow fluid machine, the rotor comprising at leastone rotor disc with a plurality of side entry channels provided in theperiphery thereof for receiving the root portions of a plurality of sideentry rotor blades having radial cooling bores extending from the rootportions through the vane portions of the blades, a passageway extendingaxially and disposed radially inwards of each of the root portions, saidpassageways communicating with the cooling bores and being capable ofconducting a flow of cooling fluid therethrough, steeples betweenadjacent channels on the periphery of the disc, a chamber disposedradially outwards of the steeples and between adjacent blades, andsealing means closing the downstream end of the passageways, theimprovement comprising: a sideplate associated with each pair ofadjacent blades and disposed on one side of said pair of blades forsealing one end of said chambers between adjacent blades; each rotorblade being provided with an extended blade neck portion, a bladeplatform portion, said platform having a ledge on its downstream sidedefining a generally radially inwardly directed groove, a portion ofeach groove being more radially inward and said radially inward sectionsdefining a generally circumferentially extending section of the groove;said groove sections at one side of any of said rotor blades, beingcomplementary to the groove sections at the other side of another rotorblade whereby when two rotor blades are positioned adjacent each other acontinuous generally U-shapEd groove is defined for securing each sideplate on the downstream side of two respective adjacent blades; saidsideplate having a body portion having edges to slidably fit within theradially outer groove sections of said U-shaped groove configurationbetween adjacent rotor blades, and arms extending generallycircumferentially from a radially inward portion of said body and havingradially outer edges of said arms shaped to snugly fit within theradially inward groove section of said U-shaped groove; and lockingmeans for securing said sideplate against unlimited radial inwardmovement with respect to said disc.
 8. The structure recited in claim 7in which said arms of said sideplate are sized and shaped to engage saidside sections of said blade neck during rotation of said rotor disc insuch a manner that the centrifugal force acting on the sideplate isborne by said arms with said body of said sideplate radially outward ofsaid arms being in tension.
 9. The structure recited in claim 7 in whichsaid radially inward groove sections are bevelled in a radiallydivergent direction, and said arms of said sideplate are provided withbevelled radially outward edges complementary in shape to the bevellingof said radially inward generally circumferentially extending groovesections.
 10. The structure recited in claim 7 in which said lockingmeans is a removable member extending through an intermediate portion ofsaid body of said sideplate in a position to engage the top of the rotordisc steeple between said pair of adjacent blades when said rotor discis at rest or at low speed rotation.
 11. The structure recited in claim8 in which said body portion of said sideplate is sized such that duringhigh speed rotation of said rotor disc a clearance will exist betweenthe radially outward edge of said body and the opposite face of saidU-shaped section of said groove.
 12. The structure recited in claim 10in which said removable member is a lock rivet.